The Anticancer Agent Chaetocin Is a Competitive Substrate and Inhibitor of Thioredoxin Reductase

Abstract

We recently reported that the antineoplastic thiodioxopiperazine natural product chaetocin potently induces cellular oxidative stress, thus selectively killing cancer cells. In pursuit of underlying molecular mechanisms, we now report that chaetocin is a competitive and selective substrate for the oxidative stress mitigation enzyme thioredoxin reductase-1 (TrxR1) with lower K m than the TrxR1 native substrate thioredoxin (Trx; chaetocin K m ¼ 4.6 ± 0.6 mM, Trx K m ¼ 104.7 ± 26 mM), thereby attenuating reduction of the critical downstream ROS remediation substrate Trx at achieved intracellular concentrations. Consistent with a role for TrxR1 targeting in the anticancer effects of chaetocin, overexpression of the TrxR1 downstream effector Trx in HeLa cells conferred resistance to chaetocin-induced, but not to doxorubicin-induced, cytotoxicity. As the TrxR=Trx pathway is of central importance in limiting cellular reactive oxygen species (ROS)-and as chaetocin exerts its selective anticancer effects via ROS imposition-the inhibition of TrxR1 by chaetocin has potential to explain its selective anticancer effects. These observations have important implications not just with regard to the mechanism of action and clinical development of chaetocin and related thiodioxopiperazines, but also with regard to the utility of molecular targets within the thioredoxin reductase=thioredoxin pathway in the development of novel candidate antineoplastic agents.

Anti-leukemia activity of chaetocin via death receptor-dependent apoptosis and dual modulation of the histone methyl-transferase SUV39H1

“…The fact that (i) chaetocin has been reported to be a competitive inhibitor of thioredoxine (Trx) for Trx reductase activity (TrxR1); 43 (ii) TrxR/Trx pathway is central in limiting ROS production; and (iii) chaetocin may exert anticancer effects via ROS generation (Isham et al 19 and this study) indicates that TrxR1 inhibition by chaetocin may at least partially explain ROS-mediated anticancer activity. However, this hypothesis does not exclude the role of the direct inhibition of SUV39H1 in chaetocin-induced apoptosis.…”

Antihepatoma activity of chaetocin due to deregulated splicing of hypoxia-inducible factor 1α pre-mRNA in mice and in vitro

“…We first examined whether Suv39H1, oxidative stress, or thioredoxin reductase-1 is involved in HIF-1a suppression. [12][13][14] However, HIF-1a expression and the chaetocin effect occurred regardless of these factors (Fig. 4A-C).…”

“…13 Mechanistically, it was proposed that chaetocin produces oxidative damage in myeloma cells by inhibiting the antioxidant enzyme thioredoxin reductase. 14 However, little is known about the effects of chaetocin on solid tumors, and thus we tested the anticancer activity of chaetocin against solid tumors. Here we demonstrated that chaetocin has antiangiogenic and anticancer activities in hepatoma and fibrosarcoma grafts, and that these actions of chaetocin are due to HIF-1a down-regulation caused by the deregulation of HIF-1a premessenger RNA (pre-mRNA) splicing.…”

Chromatin-targeting small molecules cause class-specific transcriptional changes in pancreatic endocrine cells

“…To target other classes of chromatin-modifying enzymes, compounds were chosen that have mostly been previously described: as HKMT inhibitors, we used chaetocin (16), a nonspecific compound originally described as selective for SU(VAR)3-9 and later shown to inhibit G9a (17) and thioredoxin reductase (18); BIX-01294 (19,20), a G9a/GLP-specific compound, and its active analog BRD-K62233722. DNMT inhibitors were 5-azadeoxycytidine (decitabine) (21), zebularine (22), and RG-0108 (23).…”